Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$112.98	9.785%	$124.0351	$124.04	$124.05	$124.00
Purchase #2	$99.28	4.606%	$103.8528	$103.85	$103.85	$103.90
Purchase #3	$106.89	11.726%	$119.4239	$119.42	$119.40	$119.40
Purchase #4	$56.76	13.470%	$64.4056	$64.41	$64.40	$64.40
Purchase #5	$43.85	4.816%	$45.9618	$45.96	$45.95	$46.00
Purchase #6	$223.29	13.595%	$253.6463	$253.65	$253.65	$253.60
Purchase #7	$188.95	12.318%	$212.2249	$212.22	$212.20	$212.20
7 purchase totals =	$832.00		$923.5504	$923.55	$923.50	$923.50